Amazon is making online shopping even more enticing with the addition of Sunday deliveries, and even better, Amazon Prime members can take advantage of the new shipping availability as part of the free two-day shipping option that comes bundled with the subscription.

Sunday delivery is available now in the New York and Los Angeles metropolitan areas. Next year, Amazon says it will expand the service to “a large portion of the U.S. population,” including Dallas, Houston, New Orleans and Phoenix.

Subscribers to Amazon Prime don't have to do anything differently to receive the Sunday deliveries. The $79 per year membership program already includes free two-day shipping, and orders placed on Friday will now show up on Sunday in supported areas.

Amazon says it's working with the U.S. Postal service on the Sunday deliveries, but the terms of the deal were not disclosed. A Postal Service spokeswoman told the Wall Street Journal that the agency already has a “flexible” workforce in place for Sunday deliveries, so no additional workers were necessary in the New York and Los Angeles markets. However, the spokeswoman said the postal service would look at staffing changes in other markets if the program expands.

Saturday delivery options are unchanged. Amazon still relies on FedEx for Saturday service, at a cost of $7.99 and up per item for Prime members.

One less reason to go out shopping

The addition of Sunday delivery is one of several Amazon efforts to cut down on delivery times. The online retailer offers same-day delivery in 11 markets, and delivers to storage lockers in certain areas. But same-day delivery is difficult to scale in smaller markets, and some brick-and-mortar retailers that previously hosted Amazon lockers have turned their backs on the service, probably after realizing it was undermining their own businesses.

Expanding delivery to the weekend could be a much more reliable way to encourage online shopping toward the end of the week. If customers know they'll have an item in time for the following work week, they may be more inclined to skip a trip to an actual store on their days off.

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